| Due to the excellent processing and mechanical properties of polymers and ordering structures of liquid crystals (LCs), crosslinked liquid crystalline polymers (CLCPs) become an important branch of stimuli-responsive materials. Compared with other stimuli such as heat, electric field, magnetic field, and pH variations, light attracts more attention because it is environment-friendly, remotely controllable and instantly operatable. Since photodeformable CLCPs, especially CLCPs that undergo photoinduced three-dimensional deformation (bending),were developed, many researchers have devoted in making use of CLCPs to intelligent actuators. However, difficult preparation methods, slow bending speed, small photoinduced stress, weak mechanical strength, and their monotone deformation mode seriously restrict their applications.To discuss the factors that influence the bending properties, four different LC monomers and crosslinkers were prepared. It was found that the polymerizable mixtures which contain C9A monomer show a more stable nematic phase with a broader temperature range (the maximum range is over 60℃), because the mesogen of C9A consists of three phenyls with a high aspect ratio. This is very convenient for the preparation of CLCPs.A serious of CLCP films with different concentrations of azobenzene chromophores, different crosslinking densities and different thicknesses were prepared.Before irradiated with UV light, the elastic modulus (EM) of the CLCP films (thickness:20μm, azobenzene concentration:10%) parallel to the mesogens alignment direction was four times higher than that perpendicular to the mesogens alignment direction. After the UV light irradiation, the anisotropy of EM in the two directions disappeared. It is the first time to characterize the change in mechanical properties of the CLCP films during the photochemical phase transitions.With the incorporation of the LC monomer without azobenzene moieties, the concentration of azobenzene moieties in CLCP films was turned freely and the optical path along the thickness direction in the films became longer. Therefore the films with lower concentrations of the azobenzene moieties have excellent photoinduced bending and unbending properties because of larger deformable regions generated. The photoinduced bending speed and stress of the films with the thickness of 20μm and the azobenzene concentration of 20% were 5 and 5.7 times higher than previously reported CLCP films (the azobenzene concentration of 100%). At the same time, the ultimate thickness of the films that can take place the photoinduced bending was enhanced a lot. Previously reported CLCP films have no photoinduced bending properties when the thickness was 30μm. However, the photoinduced bending speed and stress of the CLCP films with the azobenzene concentration of 20% were 4.5°·s-1 and 380 kPa when the thicknesses was 60μm. High-performance CLCP films which have both excellent photoinduced bending properties and strong mechanical strength were successfully prepared. According to the photoinduced bending behavior of the CLCP films floating on the water surface and the thermodynamics deduction, the conversion efficiency from light energy to mechanical energy was calculated out to be about 0.033%.With the help of the high-performance CLCP films and the elaborate design, a full light controlled micropump was firstly prepared. The pumping rate and the maximum pressure the pump could endure was 2.13μL·min-1 and 200 Pa respectively. The energy conversion efficiency of the pump was about 0.0024%. By making good use of unsymmetrical deformation principal, ring-shape laminated film of CLCPs and polyethylene was prepared. The ring-shape laminated film showed "ring-opening" and "ring-closing" motions upon the irradiation of UV and visible light, which are similar to the actions of human hand.Furthermore, a light controlled microrobot arm which can grasp, lift, move, and place objects was successfully prepared. In additional, by the modification of the molecular structures, we developed new CLCP films showing bending and unbending behavior totally upon the irradiation of visible light instead of UV light which is very harmful to our health. According to the similar preparation method of UV-controlled microrobot arm, visible light manipulated microrobot arm which could fulfill the manipulating actions was also prepared. This visible light controlled microrobot is safer and more environment-friendly. Because the stimulating source is visible light, the actuating materials have better aging-resisting and repeatable properties. |
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